# Price-Return Index

`D03-F04-A01` · Index and Benchmark Engineering → Return Variants · archetype `record-transform` · difficulty 2/5 · verification **verified**

Full page: https://docs.thefintechbuilder.com/index-and-benchmark-engineering/return-variants/price-return-index/
Agent skill: `npx skills add IslamBaraka90/Fintech-Algorithms-Library` — https://docs.thefintechbuilder.com/guides/agent-skill/

## Install and import

```bash
npm install fintech-algorithms
```

```ts
import { calculate } from "fintech-algorithms/index-and-benchmark-engineering/return-variants/price-return-index";
```

## Signature

```ts
calculate(data)
```

Level series from price returns alone, ignoring dividends. The number most often quoted, and the one that understates long-horizon performance.

## Parameters

| Name | Type | Required | Notes |
| --- | --- | --- | --- |
| `data` | `{ prices: number[]; baseLevel: number }` | yes | Constituent or index prices in chronological order. `baseLevel` is the index value at the start of the series; it scales the level but never the returns. |

## Returns

`{ returns, levels, endingLevel }`

Period returns, the level series, and the final level.

## Errors

- When fewer than two prices are supplied — throws

## Complexity

Time `O(n)`, space `O(n)`.

## Worked example

This is the worked example published in the article, replayed by the test suite on every run. The output cannot drift.

### Input

`data`:

```json
{
  "prices": [100, 102, 101, 104, 103.5, 106],
  "baseLevel": 1000
}
```

### Call

```ts
calculate(data)
```

### Returns

object with 3 fields: returns, levels, endingLevel

```json
{
  "returns": [0.02, -0.009804, 0.029703, -0.004808, 0.024155],
  "levels": [1000, 1020, 1010, 1040, 1035, 1060],
  "endingLevel": 1060
}
```

## Verification and provenance

Tier: **verified** (via input-expected).

The worked example below is the figure published in this algorithm's article, replayed and asserted by the test suite on every build. The arithmetic cannot drift without the build failing.

Both tiers guarantee the signature. Full explanation: https://docs.thefintechbuilder.com/guides/verification/

Generated from the docs.json payload shipped inside fintech-algorithms@0.13.1.
The signature and parameter list are checked against the compiled implementation at build time,
so a description that contradicts the code fails the build rather than reaching this file.

## Links

- Article (how it works, step by step): https://thefintechbuilder.com/index-and-benchmark-engineering/return-variants/price-return-index/
- Implementation source: https://github.com/IslamBaraka90/Fintech-Algorithms-Library/blob/main/src/index-and-benchmark-engineering/return-variants/price-return-index/impl.ts
- Package on npm: https://www.npmjs.com/package/fintech-algorithms
- Domain index for agents: https://docs.thefintechbuilder.com/index-and-benchmark-engineering/llms.txt